The present invention relates generally to a reed valve and, more particularly, to a reed valve suitable for supplying air to an intake system or an exhaust system of an engine.
Generally, reed valves are used for supplying air to an intake system or an exhaust system of an engine. In an intake system of a two-cycle engine, for example, a reed valve is disposed in an intake pipe connected between a carburetor and a crankcase so that a negative pressure produced by vertical movements of a piston is utilized to cause air/fuel mixture to be drawn via the reed valve into the crankcase for eventual combustion within a combustion chamber of the engine. The reed valve also shuts off the flow of the mixture into the crankcase when the crankcase has a high internal pressure.
In a secondary air supply apparatus of an engine often used to meet the requirements under the exhaust emission control regulations, a reed valve is disposed in a connector tube connecting an air cleaner and a pipe of an exhaust system. A pressure difference between an upstream side and a downstream side of the reed valve, which is created in the exhaust system due to pulsation of exhaust gases, is utilized to cause air to be drawn from the air cleaner via the reed valve into the exhaust gases in the exhaust system for re-combustion of exhaust gases so that unburnt components in the exhaust gases are caused to burn. The reed valve also prevents a back-flow of exhaust gases to the air cleaner when the pressure of the exhaust system is high.
FIGS. 5 through 8 show a conventional reed valve used in a secondary air supply system of an engine. The conventional reed valve 1 includes a plate-like support base 2 made of metal such as aluminum and having a generally rectangular shape when viewed in plan. The support base 2 has a valve port 3 formed at a substantially central portion across the thickness thereof for the passage therethrough of a fluid. The valve port 2 also has a generally rectangular shape when viewed in plan. An outer peripheral portion of the support base 2 forms a mount portion 2a adapted to be mounted, in an embraced manner, in an attachment groove 4 (FIG. 8) formed in an object, such as a mounting portion of a connector pipe of the engine or a case mounted on the mounting portion of the connector pipe. On a surface of the mount portion 2a, particularly both an upper surface and a lower surface of the outer peripheral portion of the support base 2, a first gasket portion 5 formed by a thin film of elastic material such as rubber is provided. The first gasket portion 5 has on its upper and lower surfaces a pair of annular projections 5a, 5a, respectively, so as to prevent the fluid from leaking outside the device when the fluid passes through the valve port 3. A second gasket portion 6 formed by an elastic material such as rubber is provided on an inner peripheral surface of the valve port 3 and both on upper and lower surfaces of a central portion of the support base 2 contiguous to the valve port 3. On an upper side of the second gasket portion 6, a generally hollow rectangular frame-like valve seat 6a extending around the valve port 3 is formed.
A substantially rectangular reed piece 7 is disposed on an upper surface of the support base 2 and normally closes the valve port 3. The reed piece 7 is adapted to open and close in response to the pressure of the fluid passing through the valve port 3. A reed stop 8 is disposed on an upper side of the reed piece 7 so as to limit or define an open position of the reed piece 7. The reed piece 7 and reed stop 8 are clamped at one end (left end in FIG. 5) to the upper surface of the support base 2 in a cantilevered fashion by a suitable clamp means such as an attaching screw 9 threaded into the support base 2 from the lower surface thereof.
The reed piece 7 operates to allow the fluid to pass through the valve port 3 in one direction from below to above and to block the flow of the fluid in the opposite direction. The reed piece 7 is formed from a resilient sheet of metal or plastic.
The reed stop 8 is formed from a rigid metal and bent at an angle such that the distance from the upper surface of the support base 2 has a maximum value at a free end (right end in FIG. 5) of the reed stop 8.
In the reed valve 1 of the foregoing construction, as shown in FIG. 8, the upper and lower annular projections 5a of the first gasket portion 5 formed on the mounting portion 2a of the support base 2 are fully squeezed out of shape by being compressed between two opposed rigid surfaces of the attachment groove 4, so as to form a seal surface extending around the mount portion 2a. By the seal surface, it is possible to prevent leakage of the fluid which may otherwise occur when the fluid is passing through the valve port 3. As shown in FIG. 5, the reed stop 8 secures a static flow rate by increasing the amount of lift (i.e., the distance from the valve seat 6a) of the reed piece 7 when the reed piece 7 is in the open state.
As indicated by solid line shown in FIG. 5, the reed piece 7 is normally in contact with the valve seat 6a and thus closes the valve port 3 of the support base 2 from the upper side thereof. Furthermore, by a pressure difference created between an upper side and a lower side of the reed valve 1 due to pulsation of exhaust gases, the reed piece 7 is caused to oscillate between the solid-lined closing position in which the reed piece 7 is in contact with the valve seat 6a at a lower surface thereof to thereby close the valve port 3, and the phantom-lined open position in which the reed piece 7 is in contact with the reed stop 8 at an upper surface thereof to thereby open the valve port 3. Thus, the reed valve 1 is constructed to allow the flow of the fluid in only one direction from below to above of the valve port 3 and to block the flow in the opposite direction.
The conventional reed valve 1 has a problem, however, that vibrations generated during opening and closing operations of the reed piece 7 are transmitted to the attachment groove 4, thereby causing the engine to produce a high level abnormal sound or noise. This problem becomes significant when the engine is operating at relative low speeds where the high level noise is offensive to the ear.
With the foregoing problem in view, it is an object of the present invention to provide a reed valve that is capable of suppressing transmission of vibrations produced by repetitive opening and closing operations of a reed piece thereby to surely prevent generation of an abnormal sound or noise.
To achieve the foregoing object, according to the present invention, there is provided a reed valve which is equipped with a vibration suppressing means for suppressing transmission of vibrations, produced by repetitive opening and closing operations of a reed piece, to a fixed mounting portion of, for example, an engine part.
The vibration suppressing means may comprise an elastic annular projection formed on an outer peripheral surface of a gasket fitted around an outer peripheral surface of a valve plate and a pair of upper and lower surfaces of the gasket, or only on the outer peripheral surface of the gasket, the elastic annular projection being elastically engaged with the fixed mounting portion when the outer peripheral portion of the valve plate is mounted to the fixed mounting portion. The annular projection elastically engaged with the fixed mounting portion is able to reduce a contact area between the outer peripheral portion of the valve plate and the fixed mounting portion. Further, when subjected to vibration from the reed piece, the annular projection elastically deforms to thereby absorb the vibration before the vibration is transmitted to the fixed mounting portion.
A cantilevered reed stop clamed to the valve plate together with the reed piece for defining an open position of reed stop may have an arch-shaped portion projecting outward away from the valve plate and extending diametrically across over the valve port. The arch-shaped portion of the reed stop preferably has an apex corresponding in position to a central portion of a valve port formed in the valve plate. By virtue of the arch-shaped portion, a maximum amplitude of oscillation of the reed piece during opening and closing operations occurs at a position corresponding to the central portion of the valve port. This means that the distance from a source of maximum vibration to the fixed mounting portion is made longer than that of the conventional reed valve wherein a reed stop is bent at an angle to the valve plate so that the maximum amplitude of oscillation of the reed piece occurs at a free end thereof. By using the arched reed stop, the amount of lift of the reed piece at the free end thereof can be reduced with the result that a shock or impact produced when the reed piece free end impinges on a surface of the valve plate is reduced.